Q: Why are there so many kinds of dryers, and where should I start to learn something about them?
A: Material handling is the greatest concern in dryer selection. Most dryers dry, some better than others, but it's essential that any material enter one end of the dryer, leave the other, and not delay too long in passage. Most particulate solids dryers are derived from mixing or material handling equipment. For instance, the rotary vacuum dryer is a jacketed and evacuated ribbon mixer, the double-cone dryer is a jacketed double-cone mixer, the pneumatic flash dryer is a heated pneumatic conveyor, and the spray dryer is a heated shot [or prilling] tower. In order of priority, dryers are selected for: 1] personnel and environmental safety, 2] the final product's quality and moisture attainment, 3] material handling capability, 4] material handling versatility, 5] heat and mass transfer characteristics, and 6] investment and operating costs.